Ladies and gentlemen, the solution is:
$ ./configure --with-oracle-headers-path=/usr/include/oracle/11.2/client64/ --with-oracle-lib-path=/usr/lib/oracle/11.2/client64/lib/
$ make
$ make install
At least this compiles without error. now let's turn to the R package itself:
$ export LD_LIBRARY_PATH=/usr/lib/oracle/11.2/client64/lib:$LD_LIBRARY_PATH
$ R CMD INSTALL ROracle_1.1-7.tar.gz
Details can be found here.